1. Field of the Invention
The present invention relates to a steering wheel with an airbag device accommodating an airbag for occupant at a driver's seat. It is to be noted that in this specification, upper and lower directions are respectively specified, as a top end side of the steering wheel is an upper side, and as a bottom end side is a lower side, when a steering wheel is in a neutral state in which a vehicle moves straight (i.e. a neutral position of the steering wheel), in a top view of the steering wheel. And, a direction crossing the vertical direction is defined as a transverse direction. Further, forward and backward directions are respectively specified, as a driver's side of the steering wheel is a foreside and a counter-driver's side is a backside.
2. Description of the Related Art
Conventionally and up to now, as a steering wheel of a vehicle such as an automobile, a steering wheel provided with an airbag device has been employed. The steering wheel is made of the airbag device and a wheel main body portion in a state in which the airbag device is removed. The airbag device corresponds to a module structure provided with an air bag, an inflator configured to supply an inflation gas to the airbag and a housing portion configured to house the airbag in an uninflated state.
The housing portion of the airbag device is constructed with a case body configured to accommodate a folded airbag and an inflator or the like, and a cover body that is mounted to the case body in a state in which the case body is covered therewith, the cover body being configured to cover the folded airbag. In addition, on an inner side of the cover body, a vulnerable portion which breaks when the airbag deploys is formed.
As a structure of removably supporting an airbag module by a wheel main body portion, there has been employed a structure of mounting a plate of which a lower limit position in a lower direction is specified with a stepped bolt for the airbag module, for example, and then, the mounting plate is secured to a spoke portion of the wheel main body portion.
In addition, recently, in place of the bolt-securing structure, there has been employed a snap-fit structure that is capable of engagingly fitting the airbag module to the wheel main body portion in a simplified manner. As a steering wheel provided with the snap-fit structure, there have been proposed a steering wheel provided with an airbag device (reference should be made to Japanese Unexamined Patent Application Publication No. 2007-50876), a steering wheel for automobile (reference should be made to Japanese Unexamined Patent Application Publication No. 2011-102052) or the like.
In so far as the snap-fit structure described in Japanese Unexamined Patent Application Publication No. 2007-50876 is concerned, it has been known that there is provided a structure of pressing down an airbag module placed at a predetermined position of a wheel main body portion to thereby produce an engaged state between a hook portion formed in the airbag module and an elastic wire rod disposed inside of the wheel main body portion. In addition, in so far as the snap-fit structure in Japanese Unexamined Patent Application Publication No. 2011-102052 is concerned, it has been known that there is provided a construction in which a hook portion is formed on a wheel main body portion's side and that an elastic wire rod that engages with the hook portion is arranged on a bottom face side of an airbag module.
In each of the inventions described in Japanese Unexamined Patent Application Publications No. 2007-50876 and No. 2011-102052, a spring, which is configured to bias the airbag module in such a direction as to be spaced from the inside of the wheel main body portion, and a switch mechanism for horn, are intervened between the airbag module and the inside of the wheel main body portion. In addition, the airbag module is biased by applying a biasing force from the spring in such as direction as to be spaced from the wheel main body portion, and at the most distant position from the wheel main body portion, a hook-engaged state is maintained. In this manner, the airbag module is mounted so as to be movable at a predetermined distance with respect to the wheel main body portion.
In the invention described in Japanese Unexamined Patent Application Publication No. 2007-50876, in the snap-fit structure employed for engagingly fitting the airbag module to the wheel main body portion's side, it has been known that there is provided a construction in which at least two or more hook portions are arranged on the bottom face side of the airbag module. In addition, although, at the time of deployment of the airbag, a tension force acts on the airbag module in such a direction as to be spaced from the wheel main body portion, even in the case where the tension force acts on the airbag module, the airbag module is constructed so as not to slip off from the engaged state by way of the snap-fit structure. As a constituent element for the sake of the objectiveness mentioned above, in order to prevent deformation even in the case where the tension force acts on the hook portion, the hook portion is constructed so as to be very rigid in structure.
That is, when the airbag starts its deployment, at the very first moment, the airbag module is pressed toward the wheel main body portion's side. However, after the airbag module cover has broken open, and airbag comes out from the airbag module, the airbag module is then strongly pulled in such a direction as to be spaced from the wheel main body portion, in such a manner as to be pulled up by the deployment of the airbag.
At this time, in order to prevent the airbag module from being spaced from the wheel main body portion, a construction to reliably maintain an engaged state between the hook portion and the elastic wire rod in the snap-fit structure is needed. As a structure for maintaining this engaged state, as has been described above, in Japanese Unexamined Patent Application Publication No. 2007-50876, the hook portion is constructed so as to be very rigid in structure.
In order to rigidly construct the hook portion, the shape of the hook portion becomes large in size, and moreover, a structure of the bottom side of the airbag module supporting the hook portion must be rigidly constructed as well. As a result, the weight of the hook portion and/or the weight of the airbag module increase.
In addition, in the case where the shape of the hook portion is formed large in size, a variety of restrictions must be applied to a layout or a construction for attaching the airbag module into the wheel main body portion. Thus, the snap-fit structure in Japanese Unexamined Patent Application Publication No. 2007-50876 results a disadvantageous structure in various points of view.
The invention in Japanese Unexamined Patent Application Publication No. 2011-102052, which was filed by the same Applicant of the present application, is directed to a construction in which the hook portion is provided at the spoke portion. Therefore, unlike the hook portion as described in Japanese Unexamined Patent Application Publication No. 2007-50876, even in the case where the hook portion and the bottom part of the airbag module are not constructed so as to be rigid in structure, the hook portion is supported by the spoke portion, thus making it possible to reliably maintain the engaged state with the airbag module.